The optimal situation for power transfer to a load connected to a line voltage (i.e. a 60 Hz alternating current (AC) power source used in a house) occurs when the load looks like a resistor to the line voltage. The power factor (PF) is a measure of how much the load looks like an ideal resistor. The power factor is defined as the ratio of the real power flowing to the load compared to the apparent power. Power factor values can range from 0 to 1 where a power factor equal to 0 would be the worst case and a power factor equal to 1 would be the best case. Power factor decreases from a value of 1 when the load has a reactive component or when the load is nonlinear.
Most ballasted lighting technologies such as white light emitting diode (WLED), organic light emitting diode (OLED), compact fluorescent lamp (CFL) and cold cathode fluorescent lamp (CCFL) do not present a linear resistive load to the incoming line voltage. Significant power losses can occur from the source of the power to where the power is ultimately consumed, at the load.
Therefore, the modern light (as well as other electronic appliances like battery chargers) are, or will very soon be, required to have power factor over 0.7˜0.9 in order to achieve better power efficiency. Despite higher initial costs, lighting solutions that provide more light output for less power (lumens per watt) are becoming economically viable due to their energy savings and long life.
Light emitting diodes (LEDs), as well as white LED (WLED), recently have become an indispensable light source due to their small size, fast lighting response, energy efficiency and long life expectancy. However, the LED still has some drawbacks that are caused by their inability to efficiently shed their waste heat. WLED lifetime decreases at an exponential rate as operating temperature increases.
In addition to the efficiency gains of modern light sources, some people use color mixing or dimming techniques (i.e. pulse width modulation (PWM) techniques) to produce a desired color. By turning different colored lamps, in close proximity, ON and OFF for various periods of time the resultant light color, as perceived by humans, can be adjusted by changing the amount of time that one lamp is on compared to another lamp. In order to avoid visible flickering the rate at which the lamps are turned ON and OFF must be above a human's ability to perceive. If there are multiple lamps in the same room and the lamps use PWM techniques to provide a mixing/dimming function then the lamps must have the same mixing/dimming frequency. If they have different dimming frequencies, the multiple lamps used in the room may appear to flicker due to the “beating” phenomenon.
Beating occurs when signals of two different frequencies are mixed together. The signal mixing process causes two other frequencies to become apparent: the sum of the two initial frequencies and the difference of the two initial frequencies. For lighting applications the difference frequency causes the most problems because, if the initial signal frequencies only vary by a few cycles per second, then the difference frequency is well within a human's ability to perceive it. This “beating” problem, no matter what type of light is used, happens very often when the dimming frequencies of different lamps are not synchronized in some way. Normal variations in electronic processing make it extremely difficult to match the frequencies of two independent groups of electronics without using very accurate, expensive techniques.